Endothelial cell seeding is an effective method of preventing thromboembolism on surfaces of cardiovascular implants and biodevices because endothelial cells release chemical agents and proteins that block platelet adhesion and fibrin formation. Stansby, G. et al., Cardiovasc Surg 2:543-548 (1994); Eberl, T. et al., Ann Thorac Surg 53:487-492 (1992); Sterpetti, A. et al., Eur J Vasc Surg 6:390-394 (1992)). Seeding of vascular graft prosthesis with endothelial cells before implantation significantly increases graft patency and survival (Ortenwall, P. et al., J Vasc Surg 11:403-410 (1990); Meinhart, J. et al., ASAIO J 43:M515-M521 (1997)). The physicochemical characteristics of biomaterial surfaces may directly influence cell adhesion and spreading as well as signaling events that regulate a wide range of biological functions, such as cell growth and extracellular matrix synthesis (Ramires, P. A. et al., Biomater 23:397-406 (2002)). Since endothelial cells adhere poorly on hydrophobic polymer surfaces (Kottke-Marchant, K. et al. J Biomed Mater Res 30:209-220 (1996)), cell detachment from biopolymer surfaces may occur upon restoring blood circulation (Williams, S. K. et al., Cell Transpl 4:401-410 (1995)). To prevent thromboembolism, polymer surface treatment to enhance endothelial cell adhesion is essential prior to the device implantation.
Deposition of protein coatings and modification of the biochemical surface properties by energetic treatments are the most common methods of improving endothelial cell adhesion on polymer surfaces. Coating polymer surfaces with proteins, such as fibronectin (Pratt, K. J. et al., J Biomed Mater Res 23:1131-1147 (1989)) and collagen (Breithaupt-Faloppa, A. C. et al, J Biomed Mater Res, Part B: Appl Biomater 76B:49-55 (2006)), has been reported to promote cellular adhesion. Fibronectin enhances adhesion at cell boundaries, while collagen produces extracellular matrix contacts (Schakenraad, J. M. Biomaterials science—An introduction to materials in medicine. Eds. Ratner B D, Hoffman A S, Schoen F J, Lemons J E. San Diego, Calif.: Academic Press; p. 141-147 (1996)). However degradation of protein coatings is a limiting factor because it leads to cellular detachment (Grinnell, F. et al., J Biol Chem 257:4888-4893 (1982)) and, in turn, platelet adhesion.
Polymer surface modification by ion implantation and plasma treatment is another means of promoting cell adhesion. Protein adsorption and endothelial cell attachment, spreading, and proliferation are influenced by both chemical and physical properties of the polymer surface (Lee, J-S. et al., Biomater 14:958-960 (1993)). Endothelial cell proliferation and spreading can be enhanced by increasing the oxygen concentration at the polymer surface (Kottke-Marchant, K. et al. J Biomed Mater Res 30:209-220 (1996); Ertel, S. I. et al. J Biomed Mater Res 24:1637-1659 (1990)). Specifically, polar surface functionalities (e.g., carboxyl groups) promote cell adhesion (Perego, G. et al., J Biomater Sci: Polymer Edn 14:1057-1075 (2003)), while ion implantation, such as Na+ (Lee, J-S. et al., Biomater 14:958-960 (1993)), Ar+ (Pignataro, B. et al., Biomater 18:1461-1470 (1997)), and F+ ({hacek over (S)}vor{hacek over (c)}ík, V. et al., J Mater Chem 5:27-30 (1995)), increases the polymer surface polarity by oxygen incorporation. Surface modification by different plasma precursors including oxygen (Ba{hacek over (c)}áková, L. et al., Biomater 17:1121-1126 (1996)), ammonia (Ba{hacek over (c)}áková, L. et al., Biomater 17:1121-1126 (1996); Pu, F. R. et al. Biomater 23:2411-2428 (2002)) and air (Pratt, K. J. et al., J Biomed Mater Res 23:1131-1147 (1989)) can also promote endothelial cell adhesion on polymer surfaces due to the presence of polar surface functionalities. In contrast to ion implantation, plasma surface modification is confined within the outermost surface layer. However, a drawback with oxygen and air plasma treatments is the degradation of the material properties as a result of chain scission.
Therefore, it is desirable to have methods for growing cells on implants without degrading the implant, particularly when high cell densities are desired, and to have implants without degradation but with high cell densities.